1. Field of the Invention
The present invention relates to a photoreceptor for use in electrophotography, and more particularly, to a photoreceptor for use in electrophotography which contains a trisazo compound.
2. Description of the Prior Art
Inorganic photoconductors such as selenium, zinc oxide and cadmium oxide have been extensively used as the principal component of the photosensitive layer of common photoreceptors for use in electrophotography. However, these inorganic photoconductors are not fully satisfactory in respect to photosensitivity, heat resistance and cycle life and so on.
Organic photoconductors are recently gaining the interest of researchers as an alternative to the inorganic photoconductors. Photoreceptors having the photosensitive layer which contains an organic photoconductor as the principal component can be manufactured fairly easily and at low cost; they can be shaped into any desired form such as a cylindrical drum or sheet; they are easy to handle and have high resistance to heat. Despite these advantages, a photoreceptor that has so far been commercialized such as the one having a photosensitive layer containing as the principal component a charge transfer complex formed of poly-N-vinylcarbazole and a Lewis acid such as 2,4,7-trinitro-9-fluorenone does not have fully satisfactory characteristics with respect to photosensitivity and cycle life.
A new approach has been taken by using two different materials that are involved in the mechanism of photoconductivity, i.e. the carrier generator material and the carrier transport material. "Function separated" photoreceptors, so called in the art which use this idea have a great latitude for the selection of materials capable of either generating or transporting charges, are fairly easy to accomplish high performance in respect to electrophotographic characteristics (e.g. charging properties, sensitivity and residual potential) and cycle life, and are adapted to the manufacture of products having any desired characteristics.
Various inorganic and organic compounds have been proposed for use as the carrier generation material. Among the inorganic carrier generation materials, amorphous selenium is well known but its performance is deteriorated under elevated temperatures due to crystallization. While many photoconductive organic dyes and pigments have been proposed, azo compounds are well known and are shown in many prior art references such as Japanese Patent Applications (OPI) Nos. 37543/2, 95033/78, 133445/78, 69148/80, 20045/82 and 205747/82 (the symbol OPI as used herein means as unexamined published Japanese patent application). However, these azo compounds are not completely satisfactory in respect to sensitivity, residual potential and stability to cyclic operation. As another disadvantage, the azo compounds do not have a great freedom in selecting a suitable carrier transport material. Therefore, none of the inorganic and organic compounds that have been previously proposed for use as the carrier generation and transport materials completely satisfy the broad spectrum of requirements of electrophotographic processing.
Gas lasers such as Ar laser and He-Ne laser, as well as semiconductor lasers have been proposed for use as light sources for image illumination of the photoreceptor. These lasers can be switched on and off by electronic means, permit high-speed high-resolution recording and are adapted to various types of recording. For these advantages, the lasers are gaining interest for use as light sources with intelligent copiers and other copying machines having video processing capabilities, as well as printers used as output devices for computers. Semiconductor lasers are of special interest because of their unique features such as the elimination of electro-to-optic converters like acoustic photocouplers, and the possibility of significant size and weight reduction. However, the semiconductor lasers produce a lower output power than gas lasers and the wavelength range of their operation is at too longer a side (.gtoreq.ca. 780 nm) to be used as light sources for the conventional photoreceptors having a shorter range of spectral sensitivities.